Systems having fixed and variable flow rate control mechanisms

ABSTRACT

The invention provides a flow control system well suited for use in intravenous fluid delivery systems comprising a flow restrictor wafer having one or more flow limiting flow restrictor paths formed thereon. The system provides fixed flow rate control. The system also provides means for selectively orienting at least two flow restrictor paths relative to the main fluid passage to varying the flow rate.

This application is a continuation of application Ser. No. 07/167,822now abandoned, filed 03/14/88.

FIELD OF THE INVENTION

The invention generally relates to systems and methods for controllingthe flow rates of fluids. More particularly, the invention relates tothe maintenance of precise and stable fluid flow rates in medical fluiddelivery systems.

BACKGROUND OF THE INVENTION

In many fluid delivery systems, it is important to be able to carefullycontrol the fluid flow rates. With respect to systems intended to beused in the intravenous administration of fluids, the precise control offluid flow rates is usually a crucial part of the therapy being providedto the patient. In the medical field, then, accuracy is an importantfeature of a flow control system. Furthermore, the intravenousadministration of fluids at uncontrolled high fluid flow rates can beharmful to the patient.

Another desirable feature of a flow control system is consistency overtime. In the medical field, it is impractical to expect a medicalattendant to be present to monitor the fluid flow rate during the entiretreatment session. A flow rate control system must thereby be capable ofmaintaining a stable flow rate while unattended for relatively longperiods of time.

Also in the medical field, as well as other environments, yet anotherdesirable feature for a flow control system is simplicity to avoidoperator error, which is more likely as the complexity of a deviceincreases. The simplicity of a flow control system also has a bearingupon the overall cost of the system, which of course is to be minimizedto the fullest extent possible without detracting from the quality ofperformance.

Many conventional intravenous fluid administration sets are providedwith manual clamping devices, such as roller clamps, which provide ameans for the operator to manually control the fluid flow rates. Rollerclamps have long served well for this purpose. However, as medicaltreatments become more sophisticated and more precise, so too should theapparatus which administer these treatments. For example, since rollerclamps are virtually infinitely variable between a fully open and afully closed position, the operator must take time to carefully adjustthe clamp to achieve the rate of flow desired. Often, a desired flowrate cannot be achieved with precision. Furthermore, the flow rate, onceachieved, can vary due to the tendency of flexible tubing used inintravenous administration systems to "creep" under the compression ofthe clamp. The flow rate initially established at the outset of thetreatment session can unexpectantly and unpredictably change during thecourse of treatment.

In portable drug administration systems (such as shown in PCTInternational Publication Number WO 861 03978, entitled Infusion Havinga Distal Flow Regulator, which is assigned to the same assignee as thisapplication), extruded glass capillary tubes are sometimes used to offera fixed resistance to flow. However, while this control technique isrelatively straightforward in its approach, it is costly to extrude acapillary tube having the desired precise flow resistance.

The need therefore still exists for cost effective systems to achievestable and precise fluid flow rate control in a fluid administrationsystem.

SUMMARY OF THE INVENTION

To achieve these and other objectives, the invention provides systemsand apparatus for precisely controlling the rate of fluid flow in asystem without reliance upon expensive or complicated controlmechanisms. The invention provides the means to control fluid floweither at a predetermined single fixed rate or within a range ofdiscrete, preselected rates.

The invention provides extremely precise and stable fluid flow ratecontrol by the use of a small, cost efficient flow restrictor wafer orchip on which one or more integrally formed flow restrictor paths areformed. The flow restrictor paths are dimensioned to achieve apreselected resistance to fluid flow to thereby control fluid flowrates.

In a preferred embodiment, the wafer is preferably formed from asemiconductor material, such as crystalline silicon. With such material,the one or more flow restrictor paths may be formed with great precisionby plasma or chemical etching techniques.

One aspect of the invention is to provide a flow restrictor wafer havingat least two flow restrictor paths, each offering a different resistanceto flow. In this arrangement, the invention provides the means forselectively directing the fluid through the flow restrictor paths. Theflow rate can thereby be controlled with precision within the range ofdiscrete flow rates associated with the flow restrictor paths.

In another aspect, the invention provides a secondary, or "back up",fluid flow rate control for a fluid delivery system having primary flowcontrol means. In this arrangement, the invention provides flowprotection means for limiting the maximum flow rate through the systemindependent of the operation of the primary control means.

Other features and advantages of the invention will become apparent uponconsidering the accompanying drawings, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fluid administration system having a flow rate protectiondevice which embodies features of the invention;

FIG. 2 is an enlarged top view of the flow rate wafer shown in FIG. 1;

FIG. 3 is a side section view of the wafer taken generally along line3--3 in FIG. 2;

FIG. 4 is a drug infusion system having a fixed flow rate control devicewhich embodies the features of the invention;

FIG. 5 is an enlarged sectional view of the control device shown in FIG.4;

FIG. 6 is a fluid delivery system having a variable flow rate controldevice which embodies features of the invention;

FIG. 7 is an exploded perspective view of the variable rate controldevice shown in FIG. 6;

FIGS. 8 is an enlarged top view of the flow rate control wafer shown inFIG. 7;

FIG. 9 is a top view of the flow rate control device shown in FIG. 6;

FIGS. 10a to 10d are a series of views showing the variable controlfeatures of the device shown in FIG. 6; and

FIG. 11 is an alternate embodiment of a variable flow rate control waferwhich embodies the features of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A fluid delivery system 10 is shown in FIG. 1. The system includes alength of tubing 12 having an inlet end 14 and an outlet end 16. Theinlet end 14 includes a connector 18 to attach the system to a source offluid 20. The outlet end 16 includes another connector 22 to attach thesystem 10 to the intended fluid delivery site.

The system 10 as just described is applicable for use in a diversenumber of environments. In the illustrated embodiment, the system 10 isintended for use in the medical field to delivery fluid for intravenousadministration to a patient.

In this environment, the tubing 12 constitutes flexible tubing made ofmedical grade plastic, like polyvinyl chloride. The connector 18comprises a conventional spike connector for attachment to the port ofan intravenous solution container 21. The other connector 22 comprises aconventional luer fitment for attachment to an intravenous catheter ofconventional design (not shown) which communicates with the circulatorysystem of the patient.

In this arrangement, the system 10 also preferably includes an inlinedrip chamber 24 and a filter 26.

The system 10 further includes a primary flow control device 28 locatedbetween the inlet and outlet ends 14 and 16 for the purpose of meteringthe flow of fluid through the tubing 12. In the illustrated embodiment,the primary flow control device 28 can take the form of a conventionalroller clamp 28. By operating the roller clamp 28, the operator can openand close the fluid path through the tubing 12. The operator can alsoadjust the roller clamp 28 between its fully opened and fully closedposition to obtain a range of desired flow rates for the fluid.

In accordance with one aspect of the invention, the system 10 includesrunaway protection means 30 for limiting the maximum flow rate throughthe tubing 12, independent of the operation of the primary flow controldevice 28. The means 30 is operative, should the primary flow controldevice 28 be incorrectly operated, malfunction, or otherwise fail tooperate properly, for automatically preventing fluid to flow through theoutlet end 16 of the system 10 above a preset maximum rate. The patientis thus protected from sudden "run-away" flow rates which would beconsidered unsafe from a medical standpoint.

In the illustrated embodiment (see also FIGS. 2 and 3), the run-awayprotector means 30 takes the form of an inline fixed flow rate controlmember 32. In accordance with the invention, this member 32 includes ahousing 34 in which a preformed flow restrictor chip or wafer 36 isencapsulated.

As shown in FIGS. 2 and 3, the wafer includes a base substrate 38 intowhich one or more flow restrictor paths 40 are formed. These paths canbe of various geometries, such as V-shaped; arcuately shaped; orrectangularly shaped, depending upon the nature of the substrate and theetching technique used. In the illustrated embodiment, a single mainflow restrictor path 40 is formed having a preselected discreteresistance to fluid flow. The flow restrictor path 40 is enclosed. Thepath 40 may be enclosed by various means, however, in the illustratedembodiment, an overlay 42 covers the base substrate 38, therebyenclosing the restrictor path 40. The wafer 36 further includes an inlet44 and an outlet 46 in the base substrate 38 which communicate atopposite ends of the flow restrictor path 40 to thereby conduct fluidinto and out of the flow restrictor path 40.

Preferably, manifold regions 48 are also preformed in the base substrate38 at the opposite ends 44 and 46 of the flow restrictor path 40 toassure a non-restricted flow on the wafer 36.

Also in the illustrated embodiment, a plurality of flow restrictor paths50, each smaller than the main flow restrictor path 40 are provided tofilter out small particulate matter during passage across the wafer 36.

The material of the base substrate 38 can be selected among thematerials on which discrete fluid flow path patterns can be formed. Suchmaterials can be metallic, ceramic, or polymer in nature. Crystallinestructures by their nature offer greater precision in the formation offlow patterns. For this reason, in the illustrated and preferredembodiment, the base substrate 38 is formed of a semiconductor material,such as crystalline silicon. In this arrangement, the main flowrestrictor path 40, the smaller flow restrictor paths 50, and manifolds48 are formed by conventional etching techniques, such as disclosed inBarth U.S. Pat. No. 4,537,680. In this arrangement, the flow restrictorpaths can be formed with a precise V-shaped geometry. The overlay 42 canbe glass, or it can comprise a semiconductor material like the structureitself. The overlay 42 can be suitably bonded to the base substrate 38,for example, by using a conventional anodic bonding process.

As shown in FIG. 2, the housing 34 in which the wafer 36 is encapsulatedhas an inlet passage 52 communicating with the wafer inlet 44 and anoutlet passage 54 communicating with the wafer outlet 46. These passages52 and 54 are, in turn, attached to the tubing 12 of the fluid deliverysystem 10.

The interior cross sectional area and the length of the flow restrictorpath 40 can be preselected in a precise manner to obtain the desiredfixed flow rate through the wafer 36. The flow rate of fluid through agiven flow restrictor path is governed by various known equations, forexample the Hagen-Pouisvelle equation. This equation can be expressedas: ##EQU1## where Q=volumetric flow rate

A=cross sectional area of the flow restrictor path

μ=fluid viscosity

ΔP=pressure drop through the flow restrictor path

L=restrictor path length

p=fluid density

g=gravitation acceleration

θ=orientation angle of the flow restrictor path relative to gravity

In the illustrated application, gravitational effects are negligible.Thus, from the equation, it can be seen that the flow through a givenflow restrictor path is controlled primarily by (1) the head height orpressure exerted on the fluid source as compared with the pressureexerted at the outlet of the system (i.e. ΔP); (2) A² /L ratio; and (3)the viscosity (μ) of the fluid. Of these, the critical control variableis the A² /L ratio. By use of a crystalline substrate, this ratio can beprecisely controlled to achieve a precise and nonvarying flow restrictorpath.

The fixed rate flow restrictor as heretofore described is applicable foruse in other fluid administration systems in the medical field. Forexample, in FIG. 4, the restrictor is part of a portable drug infusionsystem 58.

The system 58 shown in FIG. 4 includes a conventional bladder-typeinfusor 60 of the type described in Peery et al. U.S. Pat. No.4,386,929. This infusor 60 is intended to be carried or worn by thepatient while medication is intravenously delivered at a fixed,controlled rate.

The infusor 60 includes a tubular housing 62 having an outlet end 64. Afloating piston 66 is movably mounted in the housing 62. An elastomericbladder 68 is secured to the piston 66. In use, the liquid drug or othermedicament intended to be administered is conveyed into the bladder 68by a syringe or the like. Liquid is expressed from the expanded bladder68 through the outlet end 64. The piston 66 correspondingly moves towardthe outlet end 64 of the housing 62.

Tubing 70 communicates with the interior of the bladder 68 and carriesthe liquid from the bladder 68 to the patient. As in FIG. 1, in use, aconventional luer fitment 72 carried at the end of the tubing 70connects with a conventional intravenous catheter 74.

In accordance with this aspect of the invention, the system 58 includesan inline fixed flow rate control member 76 comprising a wafer 36 orchip having the same general configuration and construction (therebybeing designated with the same reference number) as shown in FIG. 2. Asbefore described, the interior diameter and length of the flowrestrictor path 40 through the wafer 36 will maintain the desired flowrate of medication to the patient.

The wafer 36 can be placed in a housing 34 as shown in FIG. 2 and belocated anywhere along the fluid path communicating with the interior ofthe bladder 68. However, in the illustrated embodiment (see FIG. 5), thewafer 36 is housed within the luer fitment 72 itself.

In this particular arrangement, the luer fitment 72 includes an inletpassage 78 communicating with the bladder 68 and an outlet passage 80communicating with the catheter 74. A seal member 82 is located betweenthe inlet and outlet passages 78 and 80. The wafer 36 is carried withinthe seal member 82 with the wafer inlet 44 communicating with the inletpassage 78 and the wafer outlet 46 communicating with the outlet passage80. All fluid traversing the fitment 72 must thus pass through the flowrestrictor path 40 of the wafer 36. The wafer 36 thus serves to regulatethe flow rate of the fluid.

Yet another fluid administration system 84 is shown in FIG. 6. Thissystem 84 shares many common elements with the system shown in FIG. 1,and these common elements share the same reference numerals.

However, as can be seen in FIG. 6 the system 84 does not include theroller clamp 28. Rather, taking the place of this element, the system 86includes a single inline variable flow rate control member whichembodies the features of the invention.

As can be best seen in FIG. 7, the inline variable flow rate controlmember 86 includes a base member 88 and a selector member 90 which ismovable carried on the base member 88. As will be described in greaterdetail below, movement of the selector member 90 (as shown by arrows inFIG. 6) serves to selectively vary the flow rate of fluid traversing thesystem 84. Movement of the selector member 90 can also serve to preventfluid flow through the system 84 altogether.

As shown in FIG. 7, the base member 88 includes a well 92. An inletpassage 94 communicates with the well 92 via an inlet port 96. Likewise,an outlet passage 98 communicates with the well 92 via an outlet port100. The opposite ends of the inlet and outlet passage, respectively 102and 104, are attached inline with the fluid tubing 12 of the system 84(see FIG. 6).

As can be seen in FIG. 7, the inlet port 96 is located generally alongthe centerline 106 of the well 92, which in the illustrated embodiment,is shown to be cylindrical in configuration. The outlet port 100 in thisarrangement is radially spaced a selected distance away from the inletport 96.

It should be appreciated that the position of the inlet and outlet ports96 and 100 would be reversed, and the well 92 could assume other than acylindrical configuration, as shown in the drawings.

An elastomeric seal member 108 occupies the well. The seal member 108includes first and second apertures 110 and 112 which extend through thebody of the member 108. The first aperture 110 registers with the inletport 96 when the seal member 108 is properly positioned in the well 96.When thus positioned, the second aperture 112 registers with the outletport 100.

A pair of locating pins 114 is positioned in the well 92. These pins 114mate with a pair of locating holes 116 in the seal member 108 to alignand retain the seal member 108 in the desired position in the well 92.

In the illustrated embodiment, the selector member 90 is rotatable onthe base member 88 about an axis generally aligned with the centerline106 of the well 92, i.e., axially aligned with the inlet port 96.

While the selector member 90 can be rotatably attached to the basemember 88 by various means, in the illustrated embodiment (see FIG. 7),the selector member 90 is rotatably affixed to the base 88 by snapfitengagement between a circumferential flange 118 on the selector member90 and a mating circumferential ridge 120 on the base member 88.

A flow restrictor wafer 122 or chip is carried by the selector member90. More particularly, projecting ridges 124 formed within the innerwall of the selector member 90 define a space 126 generallycorresponding to the shape of the wafer 122. The wafer 122 is carriedwithin this space 126, with the ridges 124 contacting the peripheraledges of the wafer 122 and preventing lateral movement thereof. Thewafer 122 is thus carried for movement in common with the selectormember 90.

The wafer 122 is constructed as above described and shown in FIGS. 2 and3, with a base substrate 38 and an overlay 42. Unlike the waferspreviously shown and described (and refer now to FIG. 8), the wafer 122includes at least two independent flow restrictor paths formed in thebase substrate. In the illustrated embodiment, four flow restrictorpaths 128, 130, 132, 134 are formed.

When the selector member 90 is rotatably affixed to the base member 88,the wafer 122 is sandwiched within the space 126 between the inner wallof the selector member 90 and the seal member 108. In this orientation,the mid point 136 of the wafer 122 is generally aligned with the axis ofrotation 106 of the selector member 90, and is therefore aligned withthe inlet port 96 itself.

Rotation of the selector member 90 thus serves to rotate the wafer 122about this axis 106, with the seal member 108 forming a sliding sealingsurface adjacent to the wafer 122.

In this arrangement, the wafer 122 includes at its midpoint an inlet 138(see FIG. 8). Radially spaced from the inlet 138 are at least twooutlets. In the illustrated embodiment, four outlets 140, 142, 144, 146are shown. Each outlet 140, 142, 144, and 146 is radially spaced fromthe inlet 138 the same distance that the outlet port 100 is spaced fromthe inlet port 96.

When the wafer 122 is sandwiched between the selector member 90 and theseal member 108, the inlet 138 of the wafer thus registers with theinlet port 96 of the base member 88 (via the aperture 110 in the sealmember 108). Rotation of the wafer 122 in common with the selectormember 90 thus serves to keep the inlet 138 of the wafer 122 inregistration with the inlet port 96 of the base member 88 (via theregistering aperture 110 in the seal member 108). Rotation also servesto place the various outlets 140, 142, 144, and 146 of the wafer 122into and out of registration with the outlet port 100 of the base member88 (via the registering aperture 122 in the seal member 108), dependingupon the position of the selector member 90 within its circular path (asshown by arrows in FIG. 6).

As can be seen in FIG. 8, the first, second, third, and fourth paths128, 130, 132, and 134 are formed in the substrate 38 of the wafer 122between the wafer inlet 138 and, respectively, the first, second, third,and fourth wafer outlets 140, 142>144, and 146. Each path 128, 130, 132,and 134 is formed with a preselected cross sectional area and length toprovide a different resistance to flow. Fluid traversing each flowrestrictor path will therefore flow at a different rate.

A scribe mark 148 on the inner wall of the selector member 90 (see FIG.7) aligns with a corresponding scribe mark 150 on the wafer 122 tolocate the wafer 122 in the desired orientation within the space 126. Inthis orientation, descriptive markings 160 on the exterior of theselector member 90 (see FIG. 9) indicate when the various wafer outletsare in or out of registration with the outlet port 100.

As shown in FIGS. 10a to 10d, the user can thus selectively orientatethe wafer 122 by rotating the selector member 90 within a range ofpositions (described as Positions A, B, C, and D) to direct the fluidflow through the flow restrictor paths 140, 142, 144, and 146 to obtainthe desired flow rate. By positioning the selector member 90 between anyof these operative positions, the wafer 122 serves to block all fluidflow through the system.

Preferably, as shown in FIG. 8 fluid manifolds 162 are formed inassociation with each flow restrictor path. If desired, filtration areas164 as above described can also be formed.

In the illustrated embodiment, the first flow restrictor path 128(Position A) meters fluid flow at a rate of 0.5 mls/hr; the second flowrestrictor path 130 (Position B) at 2.0 mls/hr; the third flowrestrictor path 132 (Position C) at 5.0 mls/hr; and the fourth flowrestrictor path 134 (Position D) at 100 mls/hr, when the system 84 isbeing operated under its normal operating conditions.

In the illustrated embodiment, all of the flow restrictor paths 128,130, 132, and 134 are V-shaped, with an included angle within the V of701/2°. The first path 128 has width measured at the top of the V of 22microns and a length of 330 microns. The second path 130 has acomparable width of 48 microns and a length of 1980 microns. The thirdpath 132 has a width of 66 microns and a length of 2760 microns. Thefourth path 134 is comprised of ten (10) parallel paths each 76 micronsin width and 2390 microns in length. As used in this application, theterm "path" can include, as in the fourth path 134, more than a singlefluid passage and can comprise a pattern of fluid passages.

The flow rates provided are discrete and precise. The user does not haveto initially adjust an infinitely adjustable roller clamp to obtain adesired flow rate. Furthermore, once selected, the flow rate set by thewafer is fixed and invariable as long as the operating conditions (suchas the effective head height ΔP) remain constant. It is not subject tochange due to "creep" in the tubing, as with a conventional rollerclamp.

The arrangement of the flow restrictor paths upon the base substrate toachieve a range of discrete flow rates can vary from that shown in FIG.8. A representative alternate arrangement is shown in FIG. 11. There, awafer 166 (constructed as shown in FIGS. 2 and 3) includes a continuousconcentric flow restrictor path 168 extending from a center opening 170outwardly in the shape of a helix. Several openings 172, 174, 176, 178are located along the path 168. Four flow restrictor paths are therebydefined, extending between opening 170 and opening 172; opening 170 and174; opening 170 and 176; and opening 170 and 178. Each flow restrictorpath has a different flow resistance due to its length and crosssectional area, thereby creating a range of discrete flow rates.

In this arrangement (as shown in FIG. 11) the center opening 170 can bealigned with an inlet port 178 located in an associated housing. Anoutlet port 180 can be arranged adjacent to the inlet port 178 on thehousing. Rotation of the wafer 166 about the inlet port 178 will bringthe outlets 172, 174, 176 and 178 into and out of registration with theoutlet port 180 to achieve the variable flow rate control as describedwith respect to FIG. 8.

Various of the features of the invention are set forth in the followingclaims.

We claim:
 1. A fluid delivery system comprisingtubing means having aninlet connectable to a source of fluid and an outlet, said tubing meansbeing operative for conveying fluid from the source to said outlet, flowcontrol means located between said inlet and said outlet and beingoperative for controlling the rate of fluid flow through said tubingwithin a range of at least two different discrete, preselected rates,said flow control means including a flow restrictor wafer having asubstrate defining at least two enclosed restrictor paths, each pathoffering a different resistance to fluid flow corresponding with saiddiscrete preselected flow rates, said flow restrictor wafer furtherincluding a wafer inlet and first and second openings, the firstenclosed restrictor path extending between the wafer inlet and the firstopening, the second enclosed restrictor path extending between the waferinlet and the second opening, and said flow control means furtherincluding selection mean for selectively directing fluid in said tubingmeans through a desired one of said flow restrictor paths, said selectormeans including a seal member which defines an inlet aperture incommunication with said flow restrictor wafer inlet and said flowcontrol means inlet and an outlet aperture in communication with saidflow control means outlet, said seal member and said flow restrictorwafer being slidable relative to each other to maintain communicationbetween said flow restrictor wafer inlet and said seal member inletaperture and to selectively establish communication between said sealmember outlet aperture and said flow restrictor wafer first or secondopening.
 2. A fluid delivery system according to claim 1wherein saidflow restrictor wafer further includes a manifold region between saidfirst opening and said restrictor paths.
 3. A fluid delivery systemaccording to claim 1wherein said flow restrictor wafer further includesthird and fourth enclosed restrictor paths, each path offering adifferent resistance to fluid flow, and third and fourth openings, thethird enclosed restrictor path extending between the wafer inlet and thethird opening, the fourth enclosed restrictor path extending between thewafer inlet and the fourth opening, and said seal member additionallyalternatively selectively establishing communication between said sealmember outlet aperture and said flow restrictor third or fourth opening.4. A fluid delivery system according to claim 1further including aselector member carrying said flow restrictor wafer, said selectormember being rotatable relative to said seal member to effectuate thesliding between said flow restrictor wafer and said seal member.
 5. Afluid delivery system according to claim 1wherein said substrate isformed of a crystalline material, and wherein said flow restrictor pathis etched in said substrate.